The present invention relates to web transport systems, and more particularly to web transport systems in heat transfer decorators.
One particularly successful type of heat transfer decorator utilizes a label carrier web which is transported past a label preheater to a decorating site, where it is heated and pressed against an article surface to transfer a heat releaseable label onto the article. Illustrative U.S. patents include: U.S. Pat. Nos. 2,981,432; 3,064,714; 3,079,979; 3,193,211; 3,208,897; 3,231,448; Re. 26,226; and 3,483,063. In designing a suitable web transport for such decorators, it is desirable that the linear motion of the web at the decorating site match the linear velocity of the article, that the labels are properly registered with the article surface during decoration, and additionally that the web be maintained at a suitable tension throughout its length.
As illustrated for example in FIG. 2 of U.S. Pat. No. 3,079,979, the label carrier web employed in these prior art decorators comprises a label bearing portion on which labels are periodically spaced, and a margin for evenly spaced pin holes. The label carrier web is fed from an unwind roll through a series of dancer and idler rolls to a metering roll, and thence past a preheater through the decorating site, further dancer and idler rolls to a rewind roll. The metering roll includes a peripheral series of pins which engage the pin holes of the web to register the speed of the web and thereby control the average web speed. Shuttle rolls are mounted astride the label transfer site on a reciprocating label shuttle, which accelerates the local web speed when extending, and decelerates the web speed when retracting. This permits a closer spacing of labels on the carrier web. The web is pulled through the various transport stations by the takeup reel, which rotates at a surface speed matching that of the metering roll. Clutch and brake assemblies at both the unwind and takeup reels, together with dancer rolls, provide torque adjustments for the reels to regulate web tension.
This prior art web transport system has proven quite satisfactory in operation, but encounters certain disadvantages attributable to the use of pin holes to register the web at the metering roll. There are economic costs associated with the punching of these holes and the additional paper needed for the pin hole margin. The need for a substantial margin to include the pin holes has the additional disadvantage that during decoration the label bearing portion of the web will be pressed against the article where this margin may offer mechanical interference. A typically encountered problem in the transport of such webs is the fraying of the edges of the pin holes, which may lead to web breakage as well as nonuniform rewind of the web. It is advantageous therefore to provide an alternative web registration system, eliminating the need for these pin holes.
One such system disclosed in U.S. Pat. No. 4,019,935 and other prior art patents, utilizes a series of indices or registration marks which are imprinted on the label web at a spacing matching the label pitch. A photoelectric detector placed adjacent the web path detects these marks and provides periodic output signals corresponding to the label pitch. It is necessary to provide a suitable location for the registration marks remote from the labels to avoid spurious signals attributable to the label. Typically, therefore such marks are imprinted on a web margin, necessitating a larger carrier web area. Thus, while these systems avoid certain of the difficulties associated with pin-feed web transports, they still suffer the problems associated with an additional web margin.
Accordingly, it is a primary object of the invention to provide an improved web transport system for use in heat transfer decorators. A related object is to design a system of this nature which precisely regulates web speed at the decorating site.
Another object of the invention is to avoid the disadvantages of a mechanical web registration system employing pin holes in the web. Specifically, it is desirable to reduce the economic costs associated with such pin holes, as well as the technical problems in transporting a web of this type.
A further object of the invention is to employ a web registration system which does not require extraneous register marks on the carrier web. It is particularly desirable to provide a carrier web of reduced area, having no substantial margin beyond the label-bearing portion.